Investigating Ex Vivo Animal Models to Test the Performance of Intravitreal Liposomal Drug Delivery Systems

Abstract

There is a strong need for innovative and efficient drug delivery systems for ocular therapy development. However, testing intravitreal drug delivery systems without using live animals is challenging. Ex vivo animal models offer an interesting alternative. We analyzed the potential of using fresh porcine eyes obtained from the local slaughterhouse as a model for testing the intravitreal biodistribution and retention of liposomes with or without polyethylene glycol (PEG) conjugation and with different surface charges. The histology of the eyes was analyzed to localize the liposomes, and it was found that liposomes with PEG absorbed rapidly on the retina (within 1 h), with positively charged and PEG-coated liposomes being retained for at least 24 h. In parallel, fluorophotometry was employed on intact eyes, to determine the pharmacokinetics of the fluorophore calcein, as a substitute for a small hydrophilic therapeutic compound. We found a 4.5-fold increase in the vitreous half-life of calcein loaded in liposomes, compared with the free solution. Retinal toxicity was addressed using murine-derived retinal explant cultures. Liposomes were non-toxic up to 500 µg/mL. Toxicity was observed at 5 mg/mL for anionic and cationic liposomes, with 2-fold and 2.5-fold increased photoreceptor cell death, respectively. Overall, we could show that important ocular drug delivery considerations such as pharmacokinetics and biodistribution can be estimated in ex vivo porcine eyes, and may guide subsequent in vivo experiments.

Pyruvate-conjugation of PEGylated liposomes effectively enhances their uptake in retinal photoreceptors

“…In the explant culture system, we do not preserve the vitreous after the culturing, so the IVT mobility of the pyruvate-liposomes was not tested. Previously we have documented the bio-distribution of similar liposomes and found that the retina could be reached after an IVT injection into ex vivo porcine eyes [40]. This is in line with similar studies [38, 41].…”

“…This would make it easier to find a suitable dosing regimen and would allow for prolonged drug exposure in the target cell, minimizing administration frequency [42]. This in turn is especially relevant for IVT injections that carry a range of potential complications [40,[43][44][45].…”

Lipid-DNA Nanoparticles as Drug-Delivery Vehicles for the Treatment of Retinal Diseases

“…Hence, it can be concluded that U4T-12 NPs presented exceptional properties regarding their adherence and distribution towards the retinal tissue. Christensen et al showed that positively charged and PEG-coated liposomes could be retained at the retina for at least 24 h in ex vivo porcine eyes [ 17 ].…”

Enhancing paracellular and transcellular permeability using nanotechnological approaches for the treatment of brain and retinal diseases

“…Surprisingly, the literature on LNPs for ocular permeability and retinal drug delivery is very limited. The team of Schipper and Paquet-Durand used LNCs to deliver CN03, a cGMP analogue, for the treatment of retinal degeneration, 55 but the drug permeation through the cornea proved to be too low for further clinical considerations. However, INV application of 2 mg mL À1 of fluorescently labeled LNCs (d = 48-72 nm, z = À0.3 to À11 mV) and liposomes showed promising improvements (Fig.…”